Posted by Trixter on February 12, 2006
I discovered last night that the right-most ISA slot (the one closest to the power supply) in my newly-unearthed 5160 won’t take the Silicon Valley Computer ADP50L 8-bit IDE controller I’ve been playing with. It will take other (short!) cards, but when I put the IDE controller into it, either the option ROM is invisible (ie. the typical BIOS ROM extension signature “55AA” not found) or won’t initialize for some reason, because I don’t get functionality out of it and the boot “banner” produced by the card is missing.
At the time, I could only conclude that:
- The IDE board is slightly awry
- The right-most ISA slot is slightly awry
- There is some technical limitation I’m not aware of
#1 and #2 are easy to accept (the hardware is two decades old), but not #3. Was there such a limitation?
As it turns out, there is! The helpful folks on the cctalk mailing list were able to point out that the data lines on slot 8 are wired to the other side of a bus buffer chip to the data lines on the other 7 slots. A card in slot 8, therefore, has to assert a special signal on the ISA connector to enable this buffer. The most common use for this slot was either an Async card, or the card you use to connect the 5161 expansion chassis.
Yes, that’s right, I said expansion chassis. If 7 slots weren’t enough for you, you could connect 8 more using a chassis that looks like the XT does, but sits on top of it. If a PC with fifteen ISA slots isn’t the most badass thing you’ve ever heard of, then you’re reading the wrong damn blog!
What’s really sad is that I’ve already filled all 7 available slots on the XT. Don’t believe me? Weep:
- Intel Above Board Plus 8 (2MB EMS)
- Sound Blaster Pro
- Serial/Parallel card
- Floppy Controller
Roland SCC-1(currently open to put in a network card)
- Hard disk controller
…and that’s it, I’m full. I would really like to put three other Above Boards in here to reach ludicrous amounts of EMS memory (theoretical limit is 56MB!), and a Central Point Option Board so that I can dupe any disk I want, and another parallel port so I can attach an LPT DAC, and an ethernet card so I can stop transferring data over LPT, and the IBM Music Feature Card, and oh hell my *other* IBM Music Feature card to double the number of voices…
Shit, I’d just max out other one, wouldn’t I? I’m sick. I need help.